JP6202897B2 - Excitation current suppression device and method - Google Patents

Description

  Embodiments described herein relate generally to an inrush current suppression apparatus and method for suppressing an inrush current generated when a transformer is turned on.

  When no-load excitation is performed by turning on the power in a state where there is residual magnetic flux in the transformer core, a large excitation inrush current flows. It is generally known that the magnitude of this magnetizing inrush current is several times the rated load current of the transformer.

  When such a large magnetizing inrush current flows, the system voltage fluctuates, and if the voltage fluctuation is large, the consumer may be affected.

  Conventionally, when a three-phase transformer with a direct grounding system with the neutral point of Y connection grounded is introduced with three single-phase circuit breakers, any one phase is introduced at the intersection of steady magnetic flux and residual magnetic flux. Then, a method for suppressing the magnetizing inrush current by adding the remaining two phases thereafter is already known.

IEEE Trans. Vol.16, No.2 2001 “Elimination of Transformer Inrush Currents by Controlled Switching -Part I: Theoretical Considerations”

  The above-described conventional charging method requires an accurate value of the residual magnetic flux of the iron core at the time of transformer interruption. In addition, information on the steady magnetic flux when the voltage is constantly applied to the transformer is also required. To calculate the magnetic flux, it is necessary to integrate the voltage.

  It is generally difficult to calculate the magnetic flux accurately. Depending on the integration start time in the voltage waveform, the integrated magnetic flux waveform is biased to be positive or negative. Further, if the voltage waveform itself does not change positively or negatively around the zero line, that is, if the DC waveform due to the offset is superimposed on the voltage waveform itself, the integrated magnetic flux waveform diverges positively or negatively.

  The purpose of the embodiment is made in view of the above-described prior art, and measures the inrush current when the transformer installed in the power system is turned on by the circuit breaker and the residual magnetic flux when the transformer is cut off. An object of the present invention is to provide an apparatus and a method for suppressing an inrush current of a transformer that can be suppressed without the need.

  In order to achieve the above object, a magnetizing inrush current suppressing device according to an embodiment of the present invention includes a circuit breaker that individually opens and closes a connection between a three-phase transformer and a three-phase AC power source in three phases. An inrush current suppression device that controls the current to be suppressed by using one phase of the AC voltage on the power supply side of the circuit breaker as a phase of interest, and measuring the voltage of the phase of interest by the voltage measuring unit. Phase detecting means for detecting a cut-off first phase in the measured AC voltage and a cut-off second phase that is a peak value of the AC voltage, and a two-phase circuit breaker other than the target phase in the cut-off first phase And an open / close pole command output means for shutting off the circuit breaker of the target phase at the shut-off second phase. The phase detection means detects a voltage peak value time point of the phase of interest as an input first phase, detects a predetermined time point after the input first phase as an input second phase, and the open / close pole command output means Closes the circuit breaker of the target phase at the first input phase and closes the circuit breakers of the two phases other than the target phase at the second input phase.

It is a block diagram which shows the connection relation of the three-phase transformer which concerns on embodiment, a three-phase circuit breaker, and a switching pole control apparatus. The state from the interruption | blocking of the 500kV transformer 3 by the circuit breaker 2 to power-on is shown, (a) is a wave form diagram which shows the transformer terminal voltage which concerns on embodiment, (b) is the transformer magnetic flux which concerns on embodiment. It is a wave form diagram which shows, (c) is a wave form diagram which shows the circuit breaker current which concerns on embodiment.

  Hereinafter, an inrush current suppression device and method according to an embodiment will be described with reference to the drawings. In addition, the overlapping description is abbreviate | omitted suitably by attaching | subjecting the same code | symbol to the same part through each figure.

  FIG. 1 is a configuration diagram showing a configuration of a power system to which the switching pole control device 5 according to the present embodiment is applied.

  The power system according to this embodiment includes a power supply bus 1, a circuit breaker 2 that opens and closes three phases individually, a transformer 3, a power supply voltage detector 4 for one phase, and a switching pole control device 5. ing.

  The power supply bus 1 is a bus of an electric power system provided with a three-phase AC power supply including a U phase, a V phase, and a W phase.

  The primary side of the transformer 3 is connected to the power bus 1 of the power system via the circuit breaker 2. The transformer 3 is a three-winding three-phase transformer that transforms, for example, a 500 kV three-phase AC voltage. The transformer 3 includes a primary winding 301, a secondary winding 302, and a tertiary winding 303. The primary winding 301 and the secondary winding 302 are Y-connected. The tertiary winding 303 is Δ-connected. The tertiary winding 303 is provided to absorb the harmonics without releasing them to the outside, and the load is generally not connected. The neutral point of the primary winding 301 and the secondary winding 302 is grounded. The neutral point of the secondary winding 302 may be high impedance grounding or non-grounding.

  The circuit breaker 2 is provided between the power supply bus 1 and the transformer 3. When the breaker 2 is turned on, the transformer 3 is turned on by the power supply bus 1.

  The power supply voltage detector 4 is provided in any target phase of the power supply bus 1. In FIG. 1, it is provided in the U phase. The power supply voltage detector 4 is an instrument for measuring the phase voltage (ground voltage) of the target phase of the power supply bus 1. The power supply voltage detector 4 is, for example, a voltage dividing device such as a voltage transformer (VT) or a capacitor-type voltage transformer (PD). The power supply voltage detector 4 is connected between the phase of interest of the power supply bus 1 and the ground. The power supply voltage detector 4 outputs the detected value as a detection signal to the magnetizing inrush current suppressing device 5.

  Based on the detection signal received from the power supply voltage detector 4, the switching pole control device 5 outputs a shut-off / closing command to the contact of each phase of the circuit breaker 2. Thereby, the circuit breaker 2 is interrupted or turned on.

  Next, the configuration and operation of the switching pole control device 5 will be described with reference to FIGS.

  FIG. 2 shows a state from the interruption of the transformer 3 by the circuit breaker 2 to the power-on. FIG. 2A is a waveform diagram showing the phase voltage of the transformer 3. FIG. 2B is a waveform diagram showing the magnetic flux of the iron core obtained by integrating the phase voltage of the transformer 3. FIG. 2 (c) is a waveform diagram showing current flowing in each phase of the transformer primary winding 301.

  The switching pole control device 5 includes a power supply voltage measurement unit 501, a phase detection unit 502, and a switching pole command output unit 503.

  The power supply voltage measuring unit 501 measures the phase voltage of the target phase of the power supply bus 1 based on the detection signal detected by the power supply voltage detector 4. The power supply voltage measurement unit 501 outputs the measured phase voltage of the target phase as a numerical value (digital value) to the phase detection unit 502.

  The phase detection unit 502 receives the phase voltage of the target phase of the power supply bus 1 measured by the power supply voltage measurement unit 501. When the circuit breaker 2 is shut off, the phase detector 502 first detects the voltage 0 of the phase voltage of the phase of interest (U phase). The phase detection unit 502 outputs the detected phase at the zero voltage point to the open / close pole command output unit 503 as the first phase (see FIG. 2) for the two phases other than the target phase.

  The opening / closing pole command output unit 503 outputs an opening command so that the phase (two phases other than the target phase) of the circuit breaker 2 is blocked in the phase detected by the phase detection unit 502.

  After the cutoff first phase, in the Δ winding 303, the V phase and the W phase are ½ magnitude and opposite phase voltages with respect to the voltage generated in the target phase (U phase). Will occur. Therefore, also in FIG. 2 (a), after the first phase of shutoff, in the V phase and the W phase, a voltage having a magnitude 1/2 and a reverse phase is generated with respect to the voltage generated in the U phase. To do. Further, in the first cut-off phase, as regards the magnetic flux, the V phase and the W phase coincide with each other as shown in FIG. As a result, after the cutoff first phase, the V-phase and W-phase magnetic fluxes coincide and change in the same manner. Further, as shown in FIG. 2C, the slight current flows in the V phase and the W phase even after the cutoff first phase is due to the hysteresis characteristics and stray capacitance of the transformer.

  The phase detector 502 further detects the voltage peak value (positive or negative maximum value) of the phase of interest (negative maximum value in FIG. 2A). The opening / closing pole command output unit 503 outputs the opening command so that the phase of interest of the circuit breaker 2 is shut off with the phase of the voltage peak value of the phase of interest detected by the phase detector 502 as the second phase of cutoff.

  Thereby, as shown in FIG. 2B, the residual magnetic flux of each phase is almost zero. That is, since the magnetic flux is 0 in all phases after the first phase of interruption, the residual magnetic flux is any phase if the remaining phase of interest is interrupted at this phase. However, it becomes almost zero. Therefore, the phase of interest may be shut off after n / 4 cycles (n is an odd number) of the power supply voltage of the bus 1 after the shut-off first phase (3/4 cycle in FIG. 2A: power supply 50 Hz) 15ms later).

  Next, when the circuit breaker 2 is turned on, the phase detector 502 first detects the voltage peak value (positive maximum value in FIG. 2A) of the target phase measured by the voltage measuring unit 501. Is output to the open / close pole command output unit 503 as the first phase. The switching pole command output unit 503 outputs a closing command to the circuit breaker 2 so that the phase of interest of the circuit breaker 2 is turned on at the inputted first phase.

  By applying the phase of interest at the phase of the voltage peak value of the phase of interest, the magnetic flux obtained by integrating the voltage of the phase of interest is positive and centered on the residual magnetic flux (approximately 0) in the first phase applied. It will change to the negative side. The reason why the voltage, magnetic flux, and current are generated in the V phase and the W phase after the first phase is the same as the reason that the voltage, magnetic flux, and current are generated in the V phase and the W phase after the aforementioned first phase. It is.

  Furthermore, after a predetermined time, the closing second phase is determined so that the remaining two phases of the breaker 2 are turned on, and the switching pole command output unit outputs a closing command to the breaker 2. The predetermined time is the time from the first phase to the time when the voltage of the phase of interest becomes 0, which is the time of n / 4 period (n is an odd number) of the power supply voltage ( In FIG. 2A, 1/4 cycle: 5 ms at 50 Hz power supply). That is, the remaining V phase and W phase are input at a phase where the voltage of the phase of interest becomes zero. By applying the V phase and the W phase at this second input phase, the V-phase and W-phase magnetic fluxes are positive and negative with respect to the respective residual magnetic fluxes (approximately 0) in the first input phase. Will change to each side. As a result, the magnetic flux peak values of U, V, and W have the same magnitude as the steady magnetic flux before the cutoff first phase. Thereby, as shown in FIG.2 (c), the transformer current (excitation inrush current) Iu, Iv, Iw of each phase is suppressed to about several amperes.

  When the circuit breaker 2 is turned on, there is a variation in closing time due to operation variations of the operation mechanism. Variations when the circuit breaker is turned on can be corrected by a control device that performs phase control by acquiring the characteristics in advance. Therefore, it goes without saying that even if there is such variation, it is possible to set the switching pole of the circuit breaker 2 to the breaking and closing phases in FIG.

(effect)
According to this embodiment, when the circuit breaker cuts off the transformer from the power source, the residual magnetic flux of each phase becomes almost 0, and when the next turn-on, the first phase is turned on at the voltage peak value. To provide an apparatus and a method for suppressing the inrush current of a transformer that can suppress the inrush current generated when the transformer is turned on without adding a facility such as a breaker with a resistor. Can do.
In the prior art, the reference phase circuit breaker is turned on at the timing when the steady magnetic flux of the reference phase and the residual magnetic flux coincide with each other. However, in this method, it is not necessary to calculate the steady magnetic flux. That is, when the circuit breaker breaks the transformer, the residual magnetic flux of each phase becomes almost zero. Therefore, when the circuit breaker is turned on next time, it is turned on at the power supply voltage peak value, and FIG. As shown in c), the current can be reduced.

  In the above description, the voltage measuring instrument 4 is provided in one phase of the power supply bus. However, it is not excluded that the voltage measuring instrument 4 is provided in three phases and these signals are input to the switching pole controller 5. That is, it is possible to provide the voltage measuring instruments 4 in the other V phase and W phase, take the voltage signals into the switching pole control device 5, and determine the phase of interest in the switching pole control device. In the above-described embodiment, the voltage measuring instrument 4 is installed in the U phase, and the shutoff and input are controlled using the U phase as the target phase. However, the voltage measuring instrument 4 is installed in the U phase and the V phase or W phase is set. As the phase of interest, it is possible to perform the same control as the above-described U phase. V-phase voltage is U-phase voltage shifted 120 degrees, and W-phase is 240 degrees shifted, so it can be easily converted from U-phase voltage to V- and W-phase voltages. It is. In that case, the degree of freedom for determining the timing of shut-off and charging is expanded.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Power supply bus line, 2 ... Circuit breaker, 3 ... Transformer, 4 ... Voltage measuring device, 5 ... Switching pole control apparatus, 501 ... Voltage measuring part, 502 ... Phase detection part, 503 ... Switching pole command output part

Claims (8)

An excitation inrush current suppressing device for controlling a circuit breaker that individually opens and closes a connection between a three-phase transformer and a three-phase AC power source to suppress excitation inrush current,
Voltage measuring means for measuring the voltage of the phase of interest with one phase of the power supply side AC voltage of the circuit breaker as the phase of interest;
Phase detection means for detecting a cutoff first phase in the alternating voltage measured by the voltage measuring means and a cutoff second phase that is a peak value of the alternating voltage;
An opening / closing pole command output means for interrupting a two-phase circuit breaker other than the target phase at the first interrupted phase, and interrupting the circuit breaker of the target phase at the second interrupted phase;
The phase detection means detects a voltage peak value time point of the phase of interest as an input first phase, detects a predetermined time point after the input first phase as an input second phase;
The switching pole command output means closes the circuit breaker of the target phase in the first input phase and closes the two-phase circuit breakers other than the target phase in the second input phase. Suppression device.   The inrush current suppression device according to claim 1, wherein the phase detection unit detects a zero point of the AC voltage measured by the voltage measurement unit as the cutoff first phase.   3. The magnetizing inrush current suppression device according to claim 2, wherein the phase detection means detects a phase after a preset time as the cutoff second phase from the cutoff first phase.   The inrush current suppression according to claim 1, wherein the phase detection unit detects a phase after a preset time has elapsed as the second input phase from the first phase when the target phase is input. apparatus. An excitation inrush current suppression method for controlling a circuit breaker that individually opens and closes a connection between a three-phase transformer and a three-phase AC power source to suppress excitation inrush current,
Taking one phase of the AC voltage on the power supply side of the circuit breaker as the phase of interest, measure the voltage of the phase of interest,
Detecting a cutoff first phase in the measured power supply side AC voltage and a cutoff second phase that is a peak value of the AC voltage;
In the breaking first phase, the two-phase circuit breaker other than the target phase is cut off, and in the breaking second phase, the breaker of the target phase is cut off,
Detecting the measured voltage peak value point of the phase of interest as the input first phase, detecting a predetermined time point after the input first phase as the input second phase,
An exciting inrush current suppression method comprising: closing a circuit breaker of the target phase at the first input phase and closing a two-phase circuit breaker other than the target phase at the second input phase.   6. The exciting inrush current suppressing method according to claim 5, wherein the first phase of cutoff is an AC voltage 0 point of the phase of interest.   The excitation inrush current suppression method according to claim 6, further comprising: detecting a phase after a preset time as the cutoff second phase from the cutoff first phase.   8. The excitation inrush current suppression method according to claim 5, wherein the two closed phases other than the target phase are phases after a preset time has elapsed from the closed phase of the target phase.

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